The present invention relates to a device and a method for regulating the lift characteristic of an exhaust charge cycle valve of an internal combustion engine.
With traditional internal combustion engines, the camshaft is driven mechanically by the crankshaft via a control chain or a control belt. To increase engine power and reduce fuel consumption, controlling the valves of the individual cylinders individually offers enormous advantages. This is possible by means of a so-called fully variable valve drive (variable control times and variable valve lift), e.g., a so-call electromagnetic valve drive.
In a fully variable valve drive, one “actuator unit” is allocated to each valve and/or each “valve group” of a cylinder. Different basic types of actuator units are currently being researched.
With one basic type (so-called lift actuators), an opening magnet and a closing magnet are allocated to one valve or one valve group. The valves may be displaced axially, i.e., opened and/or closed, by applying electric power to the magnets.
With another basic type (so-called rotary actuator), a control shaft with a cam is provided, the control shaft being pivotable back and forth by an electric motor.
Furthermore, DE 101 40 461 A1 describes a rotary actuator device for controlling the lift of a charge cycle valve. The lift is controlled here by an electric motor that is itself controlled using characteristics maps and has a shaft with a control cam that is connected to it in a rotationally fixed manner and is arranged on its rotor. During operation of the internal combustion engine, the motor swivels, i.e., swings back and forth, and the control cam periodically forces the charge cycle valve into its open position via a roller lever. The charge cycle valve is closed by the spring force of a valve spring. An additional spring is mounted on the shaft, so that the electric motor does not have to overcome the total spring force of the valve spring in opening the charge cycle valve. The forces of the valve spring and the additional spring are such that in periodic operation of the rotary actuator device, the kinetic energy is stored either in the valve spring or in the additional spring according to the position of the charge cycle valve. As a result of this measure, the power demand in operation of the rotary actuator device is reduced. The high power demand at low rotational speeds is a disadvantage of the rotary actuator device described here.
A similar device is described in U.S. Pat. No. 5,873,335 A, where a control cam of a conventional design driven by an electric motor cooperates first with the plate valve spring-loaded by a closing spring and at the other end is connected to a spring-loaded valve lifter via an opening spring arranged orthogonally to the plate valve.
A refinement of the rotary actuator device according to DE 101 40 461 A1 is described in DE 102 52 991 A1. The existing rotary actuator device is expanded here by a second actuator element (second control cam) in the opposite direction of rotation with a lower lift in comparison with the main cam. This second actuating element does not open the valve completely and is used only for small lifts in the range of low engine rotational speeds. At low rotational speeds of the internal combustion engine, the rotary actuator devices receives electric power such that the shaft swivels only in the direction of the second actuating element, whereas at high rotational speeds it is swiveled exclusively in the direction of the first actuating element. Due to the low lift, the rotary actuator device advantageously consumes less electric power at low rotational speeds.
The object of this invention is to create a device for regulating the lift characteristic of an exhaust charge cycle valve that will ensure an improvement with regard to electric power consumption by an actuator device. In particular, the subject of the invention should also ensure that the opening process of the exhaust valve will take place to the desired extent in any operating state. According to this invention, at least two setpoint paths are provided for regulating the speed of the rotor of an electric motor driving an exhaust charge cycle valve. The setpoint paths differ in that they create different amounts of kinetic energy during the valve opening process because of their design and the acceleration of the rotor associated with it and transfer this kinetic energy to the exhaust charge cycle valve via the actuator element connected to the rotor.
Thus, at least one first setpoint path is provided for generating and transferring a lower kinetic energy, whereby the setpoint path is used, for example, when a lower gas backpressure prevails in the combustion chamber due to a lower prevailing load and/or load demand (load within a predetermined load range of a lower load). Furthermore, at least one second setpoint path is provided, generating and transferring an increased kinetic energy in comparison with the kinetic energy of the first setpoint path. This is used when opening of the exhaust charge cycle valve can no longer be ensured reliably because of the higher gas backpressure in the combustion chamber affecting control of the rotor on the basis of the first setpoint path in the case of a higher prevailing load of load demand (for a prevailing load within a predetermined load range of a higher load) because the electric motor cannot supply enough power. In this case, the extra power required by the electric motor is compensated by generating an additional kinetic energy component. The kinetic energy component is generated by increasing the angular velocity of the rotor on the basis of a second setpoint path—at least in the displacement phase up to the crown point of the lift characteristic of the exhaust charge cycle valve (in particular, a predetermined period of time before the start of the valve movement, i.e., during the so-called free-running phase of the actuator element)—during the opening process in comparison with the angular velocity of the rotor (in the same displacement phase and/or in the same period of time) in the case of regulation according to the first setpoint path. To do so, in the case of the second setpoint path, the velocity specification for the rotor is increased in comparison with the velocity specification according to the first setpoint path, either from the beginning of the displacement characteristic (of the rotor) (and thus a defined period of time before the start of the actual valve movement) or from a predetermined point in time or a certain displacement path (of the rotor) (likewise a defined period of time before the start of the actual valve movement) such that in the free-running phase of the rotor, a greater kinetic energy is created in comparison with the first setpoint path.
Traditional rotary actuator devices having an electric motor as the drive unit for charge cycle valves generally compensate for interfering forces that occur at the point in time when they occur. If interfering forces are to be compensated in the form of gas backpressures, then electric motors of a higher power are generally required. Through the object of the present invention, electric motors of a reduced power (and thus energy consumption) and design size may be used in comparison with the prior art.
The present invention is preferably used in rotary actuator systems having an electric cam drive in which the cam drive driven by the rotor of the electric motor and driving the exhaust charge cycle valve has a free-running section. The free-running section ensures that the rotor, starting from the closed position of the exhaust charge cycle valve, in which the rotor acts with the smallest lift on the exhaust charge cycle valve—in particular the zero lift determined by the cam base circle—travels a defined startup distance segment and/or free-running segment on the cam base circle. The cam actuator element can be accelerated by the electric motor with the least energy input over the entire distance of the startup path section, thereby generating kinetic energy for transfer to the exhaust charge cycle valve.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.